Method for manufacturing nitride semiconductor light emitting device

Abstract

To provide a method of manufacturing a nitride semiconductor light-emitting element having a GaN quantum well layer with good surface flatness and optical characteristics by optimizing a growth pressure while suppressing the thickness of a GaN barrier layer.SOLUTION: A method of manufacturing a nitride semiconductor light-emitting device includes a quantum well layer stacking step of stacking a GaInN quantum well layer 12A containing InN, a cap layer stacking step of stacking an AlN cap layer 12B on a surface of the GaInN quantum well layer 12A, and a barrier layer stacking step of stacking a GaN barrier layer 12C on a surface of the AlN cap layer 12B, wherein growth pressures in the cap layer stacking step and the barrier layer stacking step are lower than a growth pressure in the quantum well layer stacking step.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a nitride semiconductor light-emitting device. [Background technology]

[0002] Patent Documents 1 and 2 and Non-Patent Document 1 disclose a light-emitting layer having a so-called GaInN quantum well layer, in which the quantum well layer contains In (indium). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-237281 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-235758 [Non-Patent Document 1] SMTing et al "Morphological evolution of InGaN / GaN quantum-well heterostructures grown by metalorganic chemical vapor deposition", J.Appl.Phys.94 1461-1467(2003) Summary of the Invention [Problem to be solved by the invention]

[0004] In principle, GaInN quantum wells can cover the emission wavelength range from near-ultraviolet to near-infrared, making them suitable for use as light-emitting layers in LEDs and lasers. To date, GaInN quantum well structures have been put to practical use in the wavelength range from 400 nm to 520 nm. For longer wavelengths, the In composition of the GaInN quantum well must be increased. In this case, growing the GaInN quantum well at a low growth temperature or experiencing a large lattice mismatch with the GaN substrate can significantly reduce the crystallinity of the GaInN quantum well. Therefore, ingenuity in crystal growth is generally required to form GaInN quantum wells that emit light at wavelengths of 500 nm or longer.

[0005] However, when a GaInN / GaN quantum well structure that emits light in the wavelength region of 500 nm or more is formed, many crystal defects called trench defects occur in the light-emitting layer, which leads to a decrease in light-emitting efficiency. Trench defects are defects that form as crystal growth progresses, forming ring-shaped moat-like grooves whose width increases as the crystal growth progresses. Therefore, in order to obtain high-quality GaInN quantum wells that emit light in the wavelength region of 500 nm or more, it is important to suppress the occurrence of trench defects. Several methods have been proposed to suppress the occurrence of trench defects.

[0006] A practical approach is to focus on the GaN barrier layer deposited directly on top of the GaInN quantum well layer, which requires a high InN mole fraction and therefore significantly restricts growth conditions. Specifically, trench defects have been successfully suppressed by increasing the growth temperature of the GaN barrier layer by more than 100°C higher than that of the GaInN quantum well layer. Furthermore, to prevent damage to the GaInN quantum well layer, such as desorption of In from the surface of the GaInN quantum well layer when increasing the growth temperature immediately before deposition of the GaN barrier layer, a cap layer made of AlN or AlGaN, less than a few nanometers thick, is often deposited on the surface of the GaInN quantum well layer under the same growth conditions as the GaInN layer without growth interruption. The reason for not interrupting growth here is to prevent decomposition and desorption, especially In desorption, from occurring on the surface of the GaInN quantum well layer, which would otherwise be protected, resulting in a shorter wavelength. Then, a relatively thick GaN barrier layer of 5 nm or more is grown at a temperature 100°C higher than that of the GaInN quantum well layer, which suppresses trench defects and results in a good surface with atomic layer steps. The high growth temperature of the GaN barrier layer is also thought to have an annealing effect that contributes to crystallinity improvement compared to high InN mole fraction GaInN layers, which require the use of lower growth temperatures.

[0007] We aim to apply GaInN quantum well layers emitting at wavelengths above 500 nm to the light-emitting layer of semiconductor lasers, primarily surface-emitting lasers. To achieve this, it is important to thin the GaN barrier layer. This allows for the formation of an emission layer in which as much of the GaInN quantum well layer as possible is positioned at the antinode of the optical standing wave in the surface-emitting laser cavity. This increases the optical confinement factor in the laser. Furthermore, in the case of LEDs, this can lead to improved carrier injection efficiency. However, achieving such a thin emission layer may require a GaN barrier layer as thin as 2 nm. With such a thin GaN barrier layer, the cap layer protecting the GaInN quantum well layer must already be several nanometers thick. This means that the GaN barrier layer, which can be grown at high temperatures, would be thinner, less than 1 nm, thereby negating its effectiveness.

[0008] The present invention has been made in view of the above-mentioned conventional circumstances, and aims to provide a method for manufacturing a nitride semiconductor light-emitting device having a GaInN quantum well layer with good surface flatness and optical properties, by optimizing growth conditions other than the growth temperature, specifically the growth pressure, while suppressing the thickness of the GaN barrier layer. [Means for solving the problem]

[0009] The method for manufacturing a nitride semiconductor light-emitting device of the present invention includes the steps of: a quantum well layer stacking step of stacking a quantum well layer containing InN; a capping layer lamination step of laminating a capping layer on the surface of the quantum well layer; a barrier layer laminating step of laminating a barrier layer on the surface of the cap layer; Equipped with The growth pressure in the cap layer deposition step and the barrier layer deposition step is lower than the growth pressure in the quantum well layer deposition step.

[0010] According to the configuration of the present invention, it is possible to manufacture a nitride semiconductor light emitting device having a multiple quantum well structure with excellent surface flatness and optical characteristics. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing the structure of the samples of Examples 1 to 8. [Figure 2] FIG. 2 is a time chart showing the changes in each source gas, growth temperature, and growth pressure when the sample of Example 1 is fabricated. [Figure 3] 1 shows AFM images and SEM images of each sample of Comparative Examples 1 to 3, Example 1, and Example 2. [Figure 4] 1 is a graph showing photoluminescence (PL) spectra of the samples of Comparative Examples 1 to 3, Example 1, and Example 2. [Figure 5] 1 is a schematic diagram showing the structure of an LED having a layer structure according to Example 1 and Comparative Example 1. FIG. [Figure 6] 1 is a graph showing the current-light output characteristics of LEDs having layer structures of Example 1 and Comparative Example 1. [Figure 7] 1 shows AFM images and SEM images of each sample of Example 1, Example 3, Example 4, and Comparative Example 4. [Figure 8] 1 is a graph showing photoluminescence (PL) spectra of each sample of Example 1, Example 5, Example 6, Example 7, and Comparative Example 5. [Figure 9] 1 shows an AFM image and an SEM image of the sample of Example 8. DETAILED DESCRIPTION OF THE INVENTION

[0012] A preferred embodiment of the present invention will now be described.

[0013] In the present invention, the growth pressure in the quantum well layer stacking step may be 60 kPa or more and atmospheric pressure or less, which suppresses the density of trench defects and allows linear atomic layer steps to appear, resulting in better surface flatness.

[0014] In the present invention, the growth pressure in the cap layer deposition step and the barrier layer deposition step may be 5 kPa or more and 30 kPa or less, which makes it possible to obtain better optical characteristics that exhibit good luminescence intensity.

[0015] <Example 1, Example 2, Comparative Examples 1 to 3> One example of a conventional method for forming a GaInN quantum well structure that emits light at a wavelength near 500 nm is to grow a GaInN quantum well layer that emits light at that wavelength at a relatively low growth temperature while growing a cap layer (e.g., an AlN layer, hereinafter also referred to as the AlN cap layer) to protect the GaInN quantum well layer and cover the GaInN quantum well layer. A GaN layer (hereinafter also referred to as the GaN barrier layer) is then grown under suitable growth conditions. Specifically, the GaN layer is grown at a growth temperature at least 100°C higher than the growth temperature of the GaInN quantum well layer. Meanwhile, the AlN cap layer is intended to protect the GaInN quantum well layer. Therefore, since the AlN cap layer is grown immediately after the crystal growth of the GaInN quantum well layer, it is preferable to grow the AlN cap layer under the same growth conditions as the GaInN quantum well layer without interrupting the growth after the crystal growth of the GaInN quantum well layer. Here, growth interruption refers to a state in which only NH3 (ammonia) is supplied to the reactor, and the supply of other source gases (metal oxide raw materials) is stopped.

[0016] However, as mentioned above, in the process of raising the growth temperature of the GaN barrier layer to 100°C or more, the AlN cap layer alone to protect the GaInN quantum well layer needs to be several nanometers thick, making it difficult to form a thin layer by keeping the total thickness of the AlN cap layer and GaN barrier layer to a few nanometers.

[0017] Here, another important parameter among the growth conditions other than the growth temperature is the growth pressure. Generally, when growing GaInN quantum well layers, which are susceptible to etching by thermal decomposition, a high growth pressure is preferable to suppress etching by thermal decomposition, and it is believed that high growth pressures are more likely to produce good light-emitting properties. In contrast, when growing GaInN quantum well layers at low growth pressures, impurities such as C and O are more likely to be mixed in, but the growth rate in the in-plane lateral directions (a- and m-axes) is higher than in the vertical longitudinal direction (c-axis), making it easier to obtain a good surface. In other words, the growth pressure must be optimized taking into account both surface flatness and optical properties.

[0018] For example, a GaInN quantum well layer that contributes to light emission can be grown at a high growth pressure, and an AlN cap layer for protecting the GaInN quantum well layer can be grown under the same growth conditions (growth temperature, growth pressure) as the GaInN quantum well layer without interrupting growth after the GaInN quantum well layer has grown. Then, without changing the growth temperature, the growth pressure can be lowered during growth interruption, and a GaN barrier layer that contributes less to light emission can be grown at a growth pressure lower than that of the GaInN quantum well layer and cap layer.

[0019] After careful consideration with the above policy in mind, we discovered that a high-quality GaInN quantum well structure (i.e., with good surface flatness and luminescence properties) can be formed by interrupting growth immediately before the crystal growth of the AlN cap layer, whose original purpose is to protect the GaInN quantum well layer, and by lowering the growth pressure during the growth interruption below that of the GaInN quantum well layer and growing the AlN cap layer and GaN barrier layer at the lowered growth pressure.

[0020] [Verification of the effect of different growth pressures on GaInN / AlN / GaN quantum well structures] First, we will examine GaInN / AlN / GaN quantum well structures in which GaInN quantum well layers, AlN cap layers, and GaN barrier layers are formed at four different growth pressures. Specifically, as shown in Figure 1, an undoped GaN layer 11 is crystal-grown on the surface of a GaN substrate 10. Then, on the surface of the undoped GaN layer 11, a 2-nm-thick GaInN quantum well layer 12A, a 0.3-nm-thick AlN cap layer 12B, and a 1.7-nm-thick GaN barrier layer 12C are formed as a group. This group is then crystal-grown three times to produce three pairs of GaInN multiple quantum well structures 12 at four different growth pressures.

[0021] The GaInN multiple quantum well structure 12 is formed by growing an undoped GaN layer 11 on the surface of a GaN substrate 10 having a c-plane set as the surface by MOCVD (metal organic chemical vapor deposition). Note that a GaN template grown on a sapphire substrate may be used instead of the GaN substrate 10.

[0022] Specifically, the GaN substrate 10 is first placed in a reactor of an MOCVD apparatus capable of performing the MOCVD method. Then, NH3, a source of N (nitrogen), and H2 (hydrogen), a carrier gas, are supplied into the reactor, and the temperature inside the reactor is adjusted to, for example, 1050°C. The pressure inside the reactor is then set to, for example, 90 kPa. The supply of gases into the reactor is not stopped until otherwise specified. Then, TMGa (trimethylgallium), a source of Ga (gallium), is supplied into the reactor, and a first undoped GaN layer 11A having a thickness of 0.5 μm is crystal-grown on the surface of the GaN substrate 10. The vertical direction in FIG. 1 corresponds to the stacking direction.

[0023] Next, a second undoped GaN layer 11B is deposited to a thickness of 30 nm on the surface of the first undoped GaN layer 11A using TEGa (triethylgallium), another Ga source material. Specifically, the supply of H and TMGa into the reactor is stopped. That is, the supply of source gases other than NH is stopped, and the crystal growth of the first undoped GaN layer 11A is terminated. Here, N (nitrogen) is supplied into the reactor as a carrier gas instead of H. The temperature inside the reactor is then adjusted to lower the temperature of the GaN substrate 10 to 800°C. TEGa is supplied into the reactor, and a second undoped GaN layer 11B is grown to a thickness of 30 nm on the surface of the first undoped GaN layer 11A. The supply of TEGa into the reactor is then stopped. That is, the supply of Ga source gas is stopped while continuing the supply of NH and N, and the crystal growth of the second undoped GaN layer 11B is terminated.

[0024] Next, a quantum well layer deposition process is performed to deposit a quantum well layer containing InN. Specifically, a GaInN quantum well light-emitting layer 12D, which is an emitting layer, is deposited on the surface of the second undoped GaN layer 11B formed using TEGa. The GaInN quantum well light-emitting layer 12D includes a 2-nm-thick GaInN quantum well layer 12A, a 0.3-nm-thick AlN cap layer 12B, and a 1.7-nm-thick GaN barrier layer 12C. Three periods of the GaInN quantum well light-emitting layer 12D are deposited. The three periods of the GaInN quantum well light-emitting layer 12D form the GaInN multiple quantum well structure 12. First, the GaInN quantum well layer 12A is deposited. Specifically, the temperature of the GaN substrate 10 is lowered to 690°C by adjusting the temperature in the reactor while stopping the supply of source gases of Group III elements other than N2 and NH3. At the same time, the pressure inside the reactor is adjusted to a value shown in Table 1 for growing the GaInN quantum well layer 12A.

[0025] [Table 1]

[0026] Then, the supply of TEGa, a Ga raw material, and TMIn (trimethylindium), an In (indium) raw material, into the reactor is started, and a GaInN quantum well layer 12A, which is a quantum well layer and has a thickness of 2 nm, is crystal-grown on the surface of the second undoped GaN layer 11B.

[0027] Next, a cap layer deposition step is performed to deposit an AlN cap layer 12B as a cap layer on the surface of the GaInN quantum well layer 12A. As shown in Table 1, the cap layer deposition step was performed using two patterns: one in which the AlN cap layer 12B was grown at the same growth pressure as the GaInN quantum well layer 12A without growth interruption (Comparative Examples 1 to 3), and the other in which the AlN cap layer 12B was grown with a growth interruption and a reduced growth pressure.

[0028] Specifically, the growth pressure of the GaInN quantum well layer 12A and the growth pressure of the AlN cap layer 12B were both 10 kPa in Comparative Example 1, and 80 kPa in Comparative Examples 2 and 3. Therefore, in Comparative Examples 1 to 3, in accordance with the conventional technology, the supply of TEGa and TMIn was stopped, and immediately after the growth of the GaInN quantum well layer 12A was completed, the supply of TMAl (trimethylaluminum) was started without interrupting the growth, thereby growing the AlN cap layer 12B.

[0029] In contrast, in Example 1, the growth pressure of the GaInN quantum well layer 12A was 80 kPa, and the growth pressure of the AlN cap layer 12B was 10 kPa. That is, in Example 1, the supply of TEGa and TMIn was stopped to complete the crystal growth of the GaInN quantum well layer 12A, and then a growth interruption was intentionally provided for several tens of seconds to several minutes. During this growth interruption, the growth pressure was changed from 80 kPa to 10 kPa, and then crystal growth of the AlN cap layer 12B was started.

[0030] In Example 2, the growth pressure of the GaInN quantum well layer 12A was 90 kPa, and the growth pressure of the AlN cap layer 12B was 5 kPa. As in Example 1, in Example 2, the supply of TEGa and TMIn was stopped to complete the crystal growth of the GaInN quantum well layer 12A, and then the growth was intentionally interrupted for several tens of seconds to several minutes. During this growth interruption, the growth pressure was changed from 90 kPa to 5 kPa, and then the crystal growth of the AlN cap layer 12B was started.

[0031] Next, a barrier layer deposition process is performed to deposit a GaN barrier layer 12C, which is a barrier layer, on the surface of the AlN cap layer 12B. Specifically, the supply of TMAl to the reactor is stopped to complete the growth of the AlN cap layer 12B, and then the GaN barrier layer 12C is crystal-grown on the surface of the AlN cap layer 12B at each growth pressure shown in Table 1. Again, in Comparative Example 1, Comparative Example 2, Example 1, and Example 2, when the growth pressures for the AlN cap layer 12B and the GaN barrier layer 12C are the same, the supply of TEGa is restarted immediately after the supply of TMAl is stopped without any growth interruption to start the crystal growth of the GaN barrier layer 12C. In Comparative Example 3, in order to change the growth pressures of the AlN cap layer 12B and the GaN barrier layer 12C, a growth interruption of several tens of seconds to several minutes is intentionally provided after the end of the crystal growth of the AlN cap layer 12B to change the growth pressures of the AlN cap layer 12B and the GaN barrier layer 12C. During the growth interruption, the growth pressure is changed from 80 kPa to 10 kPa, and then the crystal growth of the GaN barrier layer 12C is started.

[0032] As an example, a time chart of the formation process in Example 1 is shown in Figure 2. Note that Figure 2 shows the process up to the second GaInN quantum well layer formation process. Normally, the cap layer formation process would be performed without growth interruption to protect the GaInN quantum well layer 12A. However, to change the growth pressure from 80 kPa to 10 kPa, as shown in Figure 2, a growth interruption of several tens of seconds to several minutes is provided between the quantum well layer formation process and the cap layer formation process. After the barrier layer stacking process is performed, a growth interruption of several tens of seconds to several minutes is provided before the quantum well layer formation process of the next cycle is performed to change the growth pressure from 10 kPa to 80 kPa.

[0033] The GaInN quantum well layer 12A, AlN cap layer 12B, and GaN barrier layer 12C thus grown were considered as one group, and this group was subjected to crystal growth three times to fabricate the GaInN multiple quantum well structure 12. The supply of TEGa to the reactor was stopped when the crystal growth of the GaN barrier layer 12C in the third cycle was completed, thereby completing the fabrication of each sample. In this manner, the samples of Comparative Example 1 to Comparative Example 3, Example 1, and Example 2 were fabricated.

[0034] 3 shows atomic force microscope (AFM) images (hereinafter also simply referred to as AFM images) and scanning electron microscope (SEM) images (hereinafter also simply referred to as SEM images) of each sample of Comparative Examples 1 to 3, Examples 1, and 2. The AFM images (the images on the left in FIG. 3) allow the flatness of the surface to be determined, and the SEM images (the images on the right in FIG. 3) allow the number of trench defects to be determined.

[0035] Comparing the SEM images of Comparative Example 1 (quantum well layer: 10 kPa / cap layer: 10 kPa / barrier layer: 10 kPa) and Comparative Example 2 (quantum well layer: 80 kPa / cap layer: 80 kPa / barrier layer: 80 kPa), it can be seen that a large number of trench defects D appeared in Comparative Example 2, while trench defects D appeared at a high density in Comparative Example 1, although their area was small. In contrast, Comparative Example 3 (quantum well layer: 80 kPa / cap layer: 80 kPa / barrier layer: 10 kPa) had a larger RMS (root mean square) value than Comparative Examples 1 and 2, indicating a greater degree of surface irregularity.

[0036] In contrast, in Examples 1 and 2 (samples in which only the GaInN quantum well layer 12A was grown at a high growth pressure, and then the growth was interrupted for several tens of seconds to several minutes, exposing the surface of the GaInN quantum well layer 12A to the atmosphere in the reactor, during which the growth pressure was reduced, and then the AlN cap layer 12B and the GaN barrier layer 12C were grown without growth interruption), SEM images showed that the area and density of trench defects D were significantly reduced compared to Comparative Examples 1 to 3. Furthermore, AFM images of Examples 1 and 2 showed linear atomic layer steps on the surface, indicating that good surface flatness was obtained.

[0037] 4 shows the results of photoluminescence measurements at room temperature for the samples of Comparative Examples 1 to 3, Example 1, and Example 2. The graph in Fig. 4 shows the light emission characteristics from the GaInN quantum well layer 12A. It was found that the samples of Example 1 and Example 2 exhibited peaks with significantly higher intensity around a wavelength of 500 nm compared to the samples of Comparative Examples 1 to 3.

[0038] From the above results, it was found that a GaInN multiple quantum well structure 12 with good surface flatness and optical properties can be formed by not immediately growing the AlN cap layer 12B after growing the GaInN quantum well layer 12A, but by interrupting the growth and sufficiently lowering the growth pressure before growing the AlN cap layer 12B.

[0039] Based on the above results, two LEDs were fabricated: one having a GaInN quantum well layer 12A fabricated in the same manner as in Example 1, and the other having a GaInN quantum well layer 12A fabricated in the same manner as in Comparative Example 1. Figure 5 shows the layer structure of this LED. The difference from the sample of Example 1 (Comparative Example 1) (see Figure 1) is that an n-GaN layer 13 having a thickness of 540 nm is stacked between the GaInN multiple quantum well structure 12 and the undoped GaN layer 11, and a final GaN barrier layer 14 having a thickness of 4 nm, a p-GaN layer 15 having a thickness of 110 nm, and a p-GaN layer 16 having a thickness of 20 nm are stacked on the GaInN multiple quantum well structure 12. +The n-GaN layer 13 is doped with Si as a semiconductor impurity. + The -GaN contact layer 16 is doped with Mg as a semiconductor impurity.

[0040] The layer structure shown in FIG. 5 is a p + After growing the GaN contact layer 16, the GaInN multi-quantum well structure 12 is grown to p + The portion where the crystal had grown up to the n-GaN contact layer 16 was left in a cylindrical shape, and the surrounding area was removed by etching to expose the surface of the n-GaN layer 13. After that, a heat treatment was performed to remove the p-GaN layer 15 and the p + After activating the Mg contained in the n-GaN contact layer 16, a circular n-side electrode E1 is provided on the exposed surface of the n-GaN layer 13 so as to surround the cylindrical portion that has not been etched. + A disk-shaped p-side electrode E2 is provided on the surface of the -GaN contact layer 16. As a result, electrons and holes are injected into the GaInN multiple quantum well structure 12 via the pn junction, causing it to emit light.

[0041] 6 shows the current-light output characteristics of an LED having a GaInN multiple quantum well structure 12 fabricated by the same method as in Example 1, and an LED having a GaInN multiple quantum well structure 12 fabricated by the same method as in Comparative Example 1. It can be seen from FIG. 6 that the LED fabricated by the method of Example 1 (in which growth was interrupted after crystal growth of GaInN quantum well layer 12A to reduce the growth pressure, and then AlN cap layer 12B was grown) had a light output that was approximately 30% higher than that of the LED fabricated by the method of Comparative Example 1. It is also believed that even if an LED having the layer structure shown in FIG. 5 were fabricated by the same method as in Example 2, a result in which light output was increased compared to that of the LED fabricated by the method of Comparative Example 1 would be obtained.

[0042] <Example 3, Example 4, Comparative Example 4> [Verification of the effect of growth pressure during quantum well layer deposition on surface flatness and light emission characteristics] The verification results of Examples 1 and 2 revealed that a GaInN multiple quantum well structure 12 that emits excellent light at a wavelength of around 500 nm can be formed by interrupting the growth between the quantum well layer deposition process and the cap layer deposition process and lowering the growth pressure during the growth interruption so that the growth pressure in the cap layer deposition process and the barrier layer deposition process is lower than the growth pressure in the quantum well layer deposition process. Next, the influence of the growth pressure in the quantum well layer deposition process on the surface flatness and light emission characteristics was investigated. As shown in Table 2, samples having a GaInN multiple quantum well structure 12 were formed by varying the growth pressure of the GaInN quantum well layer 12A from Example 1 (quantum well layer: 80 kPa) to 70 kPa (Example 3), 60 kPa (Example 4), and 40 kPa (Comparative Example 4).

[0043] [Table 2]

[0044] In the fabrication of samples in Examples 3, 4, and Comparative Example 4, a growth interruption of several tens of seconds to several minutes was provided between the quantum well layer deposition step and the cap layer deposition step to change the growth pressure. In the fabrication of samples in Examples 3, 4, and Comparative Example 4, the growth pressure in the cap layer deposition step and the barrier layer deposition step was fixed at 10 kPa. In other words, no growth interruption was provided between the cap layer deposition step and the barrier layer deposition step.

[0045] 7 shows AFM images and SEM images of the surfaces of the samples of Example 1, Example 3, Example 4, and Comparative Example 4. Comparing the SEM images of each sample reveals that the density of trench defects D is suppressed in Example 1, Example 3, and Example 4 compared to Comparative Example 4. Comparing the AFM images of each sample reveals that linear atomic layer steps appear in Example 1, Example 3, and Example 4, indicating that a good crystal surface has been formed.

[0046] From the above, it was found that a GaInN multiple quantum well structure 12 having good surface flatness can be formed by setting the growth pressure of the GaInN quantum well layer 12A to 60 kPa or higher and reducing the growth pressures of the AlN cap layer 12B and the GaN barrier layer 12C. It is considered that, if the growth pressure of the GaInN quantum well layer 12A is atmospheric pressure (approximately 100 kPa) or lower, it is possible to grow a GaInN quantum well layer 12A in which atomic layer steps appear in the AFM image, as in Examples 1, 3, and 4, and in which the density of trench defects D is suppressed compared to Comparative Example 4 in the SEM image. In other words, it is preferable that the growth pressure in the quantum well layer stacking step be 60 kPa or higher and atmospheric pressure or lower.

[0047] <Example 5, Example 6, Example 7, Comparative Example 5> [Growth pressure dependence of AlN cap layer and GaN barrier layer] Next, we investigated the dependence of the AlN cap layer 12B and the GaN barrier layer 12C on the growth pressure. As shown in Table 3, based on Example 1 (cap layer: 10 kPa / barrier layer: 10 kPa), samples having a GaInN multiple quantum well structure 12 were fabricated by fixing the growth pressure of the GaInN quantum well layer 12A at 80 kPa and varying the growth pressure of the AlN cap layer 12B and the GaN barrier layer 12C to 5 kPa (Example 5), 20 kPa (Example 6), 30 kPa (Example 7), and 40 kPa (Comparative Example 5). In all samples, growth was interrupted for several tens of seconds to several minutes to change the growth pressure after the crystal growth of the GaInN quantum well layer 12A and before the crystal growth of the AlN cap layer 12B.

[0048] [Table 3]

[0049] 8 shows the results of photoluminescence measurements showing the light emission characteristics from the GaInN quantum well layer 12A in each sample of Example 1, Example 5, Example 6, Example 7, and Comparative Example 5. It was found that when the growth pressure of the AlN cap layer 12B and the GaN barrier layer 12C was 40 kPa (Comparative Example 5), the photoluminescence intensity was lower than in Examples 1, 5, 6, and 7. In other words, it was found that the growth pressure in the cap layer deposition step and the barrier layer deposition step was preferably 5 kPa or more and 30 kPa or less (Examples 1, 5, 6, and 7), which is lower than the growth pressure in the quantum well layer deposition step, and that a better light emission intensity was shown than in Comparative Example 5.

[0050] Summarizing the above verification results, we found that when growing GaInN multiple quantum well structure 12 that emits light at wavelengths of 500 nm or longer, it is important to change the growth pressure by setting the growth pressure to 60 kPa or more but not more than atmospheric pressure when growing GaInN quantum well layer 12A, 5 kPa or more but not more than 30 kPa when growing AlN cap layer 12B, interrupting growth to change the pressure after growing GaInN quantum well layer 12A and before growing AlN cap layer 12B, and setting the growth pressure to 5 kPa or more but not more than 30 kPa when growing GaN barrier layer 12C. This method is particularly useful when GaN barrier layer 12C is thin and the growth temperature cannot be increased by more than 100°C above the growth temperature for GaInN quantum well layer 12A.

[0051] Furthermore, in the present invention, increasing the growth pressure of the GaInN quantum well layer 12A significantly improved the surface flatness rather than the optical properties, while decreasing the growth pressure of the AlN cap layer 12B and the GaN barrier layer 12C significantly improved the optical properties rather than the surface flatness. This was a new finding that contradicts the conventional understanding that high growth pressures tend to provide good light emission properties and low growth pressures tend to provide good surfaces.

[0052] Example 8 On the other hand, if the GaN barrier layer 12C is thin, it is possible to increase the growth temperature higher than that of the GaInN quantum well layer 12A by a small amount. Here, in Example 8, we investigated a case where the growth temperature was increased not only for the GaN barrier layer 12C but also for the AlN cap layer 12B. As described above, the AlN cap layer 12B originally plays a role in protecting the GaInN quantum well layer 12A. In other words, considering the protection of the GaInN quantum well layer 12A, it is preferable to immediately grow the AlN cap layer 12B after the crystal growth of the GaInN quantum well layer 12A without interrupting the growth and without changing the growth temperature.

[0053] However, we intentionally interrupted the growth immediately after the crystal growth of the GaInN quantum well layer 12A, and during that time, we attempted to lower the growth pressure and increase the growth temperature. Based on Example 1, in Example 8, during the growth interruption after the quantum well layer formation process, we increased the growth temperature by 20°C from 690°C to 710°C and reduced the growth pressure from 80 kPa to 10 kPa, and then grew the AlN cap layer 12B and the GaN barrier layer 12C. As a result, as shown in the AFM and SEM images in Figure 8, the trench defects D were further reduced compared to the samples of Examples 1 to 7, and the RMS value was further reduced compared to the samples of Examples 1 to 7, indicating that good surface flatness was obtained.

[0054] Next, the effects of the above embodiment will be described.

[0055] The method for manufacturing a nitride semiconductor light-emitting device includes a quantum well layer deposition step of depositing a GaInN quantum well layer 12A containing InN, a cap layer deposition step of depositing an AlN cap layer 12B on the surface of the GaInN quantum well layer 12A, and a barrier layer deposition step of depositing a GaN barrier layer 12C on the surface of the AlN cap layer 12B, wherein the growth pressures in the cap layer deposition step and the barrier layer deposition step are lower than the growth pressure in the quantum well layer deposition step. This configuration makes it possible to manufacture a nitride semiconductor light-emitting device having a GaInN multiple quantum well structure 12 with excellent surface flatness and optical properties.

[0056] The growth pressure in the quantum well layer deposition process is 60 kPa or more and atmospheric pressure or less. This configuration suppresses the density of trench defects, resulting in linear atomic layer steps and better surface flatness (see Figure 7).

[0057] The growth pressure in the cap layer deposition step and the barrier layer deposition step is 5 kPa or more and 30 kPa or less. This configuration makes it possible to obtain better optical characteristics that exhibit good emission intensity (see FIG. 8).

[0058] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is not limited to the embodiments disclosed herein, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims. (1) The growth temperatures in the quantum well layer deposition step, the cap layer deposition step, and the barrier layer deposition step are not limited to those in the above embodiment. (2) The material of the cap layer is not limited to AlN, but may be other materials such as AlGaN. (3) The material of the barrier layer is not limited to GaN. (4) The increase in growth temperature during the growth interruption after the quantum well layer formation step is not limited to that in the eighth embodiment. (5) The number of periods of the GaInN quantum well light-emitting layers is not limited to the number in the above-described embodiment. (6) The thicknesses of the GaInN quantum well layer, the AlN cap layer, and the GaN barrier layer are not limited to those in the above embodiment. (7) The carrier gas used when forming the GaInN quantum well layer, the AlN cap layer, and the GaN barrier layer is not limited to N2, but may be H2 or a mixture of multiple gases (N2 and H2). [Explanation of symbols]

[0059] 12A...GaInN quantum well layer (quantum well layer) 12B...AlN cap layer (cap layer) 12C...GaN barrier layer (barrier layer)

Claims

1. a quantum well layer stacking step of stacking a quantum well layer containing InN; a capping layer lamination step of laminating a capping layer on the surface of the quantum well layer; a barrier layer laminating step of laminating a barrier layer on the surface of the cap layer; Equipped with a growth pressure in the cap layer deposition step and the barrier layer deposition step being lower than a growth pressure in the quantum well layer deposition step;

2. 2. The method for manufacturing a nitride semiconductor light-emitting device according to claim 1, wherein a growth pressure in said quantum well layer stacking step is 60 kPa or more and atmospheric pressure or less.

3. 3. The method for manufacturing a nitride semiconductor light-emitting device according to claim 1, wherein a growth pressure in the cap layer deposition step and the barrier layer deposition step is 5 kPa or more and 30 kPa or less.

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